Parametric study of a free-falling penetrometer in clay-like soils

A free-falling penetrometer (FFP) is a useful apparatus for providing information on the mechanical properties of soil layers, especially where the site in question is inaccessible, which is normally the situation for many seabed, river and swamp deposits. FFP tests can provide useful data such as the total depth and time of penetration and the deceleration characteristics of the penetrometer, provided it is suitably instrumented. The main quantities of interest measured in FFP tests, viz., the time and depth of penetration, depend on the mechanical properties of the soil, such as its shear strength and rigidity index, as well as those parameters associated exclusively with the penetrometer, such as its geometry and the energy with which it first impacts the soil. Potentially, these penetration data can be used to deduce strength parameters for the soil in situ, either through empirical correlations or else by application of a rigorous numerical solution for the ideal penetration problem. Arobust finite element analysis procedurewas developed at the University of Newcastle, Australia, especially for the analysis of geotechnical problems, including problems that involve soil penetration. This method of analysis is based upon the Arbitrary Lagrangian Eulerian (ALE) finite element technique and takes into account material nonlinearity and rate dependence, large deformations, changing boundary conditions, and time-dependent loading, including an allowance for dynamic forces when necessary. The present study aims to provide some numerical results describing the effect of the mechanical properties of the soil and the energy of the penetrometer on the penetration response. This goal has been achieved by performing a wide range of FFP analyses using the proposed ALE finite element method.